Data transmitter and receiver of a spread spectrum communication system using a pilot channel

ABSTRACT

An improved spread spectrum communication system includes a transmitter and a receiver utilizing a pilot channel for the transmission of pure rather than modulated PN codes for code acquisition or tracking purposes with a lower bit error rate. The pilot signal is used to obtain initial system synchronization and phase tracking of the transmitted spread spectrum signal. At the transmitter side, Walsh an orthogonal code generator, a Walsh modulator, a first PN code generator, a first band spreader, a second band spreader, finite impulse response filters, digital-to-analog converter, low-pass filters, an intermediate frequency mixer, a carrier mixer, a band-pass filter are used to transmit a spread spectrum signal. At the receiver side, a corresponding band-pass filter, a carrier mixer, an intermediate-frequency mixer, low-pass filters, analog-digital converters, a second PN code generator, an I channel despreader, a Q channel despreader, a PN code synchronization controller, a Walsh an orthogonalcode generator, a first Walsh demodulator, a second Walsh demodulator, accumulator &amp; dump circuits, a combiner, and a data decider are used to demodulate a received spread spectrum signal.

This application is a parent of a continuing reissue application filedon Apr. 16, 2003 assigned Ser. No. 10/414,203, and is a reissue of U.S.Pat. No. 5,712,869 issued Jan. 27, 1998.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application makes reference to, incorporates the same herein, andclaims all benefits accruing under 35 U.S.C. §119 from an applicationfor Data Transmitter And Receiver Of A Spread Spectrum CommunicationSystem Using a Pilot Channel earlier filed in the Korean IndustrialProperty Office on 22 Nov. 1994 and assigned Ser. No. 30743/1994.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a spread spectrum communication system,and more particularly to data transmitter and receiver of the spreadspectrum communication system using a pilot channel.

2. Background Art

Conventionally, narrow band modulation systems (such as for example,amplitude modulation, frequency modulation and phase shift keymodulation) have been used in the field of data communication. With suchsystems, demodulation at the receiver can be achieved with a relativelysmall amount of circuitry. Such systems, however, are weak due tomultipath fading and narrow band noise.

By contrast, in spread spectrum communication systems, a data spectrumis spread by a pseudo-noise code (hereinafter “PN code”) at atransmitting side, while the pseudo noise code and the data aresynchronized at a receiving side to that the adverse effects ofmultipath fading and narrow band noise can be reduced. Accordingly,spread spectrum communication systems have attracted increased attentionas a promising technique for radio frequency transmission of binarydata.

One example for such a spread spectrum communication system is disclosedin U.S. Pat. No. 5,400,359 entitled Spread Spectrum Communication Systemand An Apparatus For Communication Utilizing This System issued toHikoso et al. on 21 Mar. 1995. In Hikoso et al. '359, a pseudo noisecode is generated and multiplied by data to generate a multiplied resultwhich is then subjected to binary phase-shift key (BPSK) modulation,although other phase-shift key modulation such as, for example,differential phase-shift key modulation (DPSK) may also be used. Thepseudo noise code is also subjected to BPSK modulation, delayed by atleast one chip of the pseudo noise code, combined with a modulatedsignal, converted into a radio requency (RF) signal, and transmittedfrom an antenna. The transmitted spread spectrum signal is received at areceiving end where a complementary receiving method is provided. Inessence, the spread spectrum communication involves the art of expandingthe bandwidth of a signal, transmitting the expanded signal, andrecovering the desired signal by remapping the received spread spectruminto the original information bandwidth. The purpose of spread spectrumtechniques is to allow the system to deliver error-free information in anoisy signal environment.

In such a spread spectrum communication system however, since thespectrum of the information signal is spread by a PN code having abroader spectrum width, i order to correctly restore the informationsignal, it is necessary to synchronize the demodulation PN code which isgenerated at the receiving side with the modulation PN code which isgenerated at the transmitting side. Proper phase synchronization may beachieved when the received spread spectrum signal is accurately timed inboth its spreading PN code pattern position and its rate of chipgeneration. The phase synchronization process is typically accomplishedin two stages, i.e., an initial synchronization process for finding asynchronous phase and a process for tracking the detected phase. Inthese conventional spread spectrum receivers, however, initialsynchronization and synchronization tracking are often achieved throughcostly and complex circuitry. Moreover, we have observed that it isdifficult to adjust synchronization of the PN code at the receivingside, as the modulated PN code and not pure PN code is transmitted atthe transmitting side. Consequently, the time required to establishinitial synchronization has not effectively improved.

SUMMARY OF THE INVENTION

Accordingly, it is therefore an object of the present invention toprovide a novel and improved spread spectrum communication systemutilizing a pilot signal for establishing initial systemsynchronization.

It is another object of the present invention to provide an improvedspread spectrum communication system utilizing a pilot signal forsimplifying the synchronization process and minimizing the PN codeacquisition time.

It is also an object of the present invention to provide an improvedspread spectrum communication system including a transmitter and areceiver capable of utilizing a pilot signal for simplifying thesynchronization process and minimizing the PN code acquisition time.

It is also an object of the preset invention to provide a improvedspread spectrum communication system capable of providing thetransmission and reception of a spread spectrum signal with low biterror rates.

It is a further object of the invention to provide an improved spreadspectrum communication system capable of reducing peak-to-average powerratio (PAR) in a transmitter of a mobile communication system using atleast two channels.

To achieve the above objects of the present invention, the spreadspectrum communication system includes a novel and improved transmitterand a complementary receiver capable of establishing a pilot channel forthe transmission of pure rather than modulated PN codes for acquisitionor tracking purposes.

To achieve the above objects of the present invention, the spreadspectrum communication system is constructed to receive first and secondinput signals, to spread the first input signal with first and secondspreading code signals to produce first and second spread signals,respectively, to spread the second input signal with the first andsecond spreading code signals to produce third and fourth spreadsignals, respectively, to produce a first output spread signal bysubtracting the fourth spread signal from the first spread signal, andto produce a second output spread signal by adding the second spreadsignal to the third spread signal, so that the PAR could be reduced upona radio transmission of the first and second output spread signals.

The improved transmitter as constructed according to the presentinvention comprises a first Walsh orthogonal code generator forgenerating first and second Walsh orthogonal codes having respectiveWalsh orthogonal code systems; a Walsh orthogonal modulator formultiplying a predetermined pilot signal and data to be transmittedrespectively by the first and second Walsh orthogonal codes andgenerating Walsh- orthogonal modulated pilot signal and data; a first PNcode generator for generating first and second PN codes; a first bandspreader for multiplying the Walsh-modulated pilot signal by the firstand second PN codes, and generating I channel and Q channel bandspreaded signals; a second band spreader for multiplying theWalsh-modulated data by the first and second PN codes, and generating Ichannel and Q channel band spreaded data; a finite impulse responsefilter for finite impulse response filtering the band spreaded pilotsignals and data; a first converter for combining the I channel bandspreaded pilot signal and data, and then converting into an I channelanalog signal; a second converter for combining the Q channel bandspreaded pilot signal and data and then converting into a Q channelanalog signal; a lowpass filter for lowpass filtering the I channel andQ channel analog signals; an intermediate frequency mixer for receivingthe lowpass filtered I channel and Q channel lowpass filtering signalsand an intermediate frequency signal multiplying the I channel lowpassfiltering signal by in phase component cosW_(IF)t of the intermediatefrequency signal, the Q channel low-pass filtered signal by a quadraturephase component sinW_(IF)t of the intermediate frequency signal, andthen combining the I channel and Q channel signals which have been mixedwith the intermediate frequency; a carrier mixer for multiplying theoutput signal of the intermediate frequency mixer by a radio frequencysignal cosW_(IF)t; a bandpass filter for bandpass filtering the outputsignal of the carrier mixer; and a first amplifier for amplifying thebandpass filtered signal according to a predetermined amplificationratio for transmission via an antenna.

The complementary receiver as constructed according to the presentinvention comprises a second amplifier for amplifying a spread spectrumsignal received via an antenna; a bandpass filter for bandpass filteringthe output signal of the second amplifier; a first mixer for multiplyingthe output signals of the bandpass filter by the radio frequency signalcosW_(RF)t, and converting into an intermediate frequency signal; asecond mixer for multiplying the intermediate frequency signal by an inphase component cosW_(IF)t and a quadrature phase component sinW_(IF)tof the intermediate frequency, respectively, and then outputting Ichannel and Q channel signals from which the carrier frequency signalhas been removed; a low-pass filter for low-pass filtering the I channeland Q channel signals, respectively; an analog-digital converter forconverting the low-pass filtered I channel and Q channel signals intodigital signals; a second PN code generator for generating first andsecond PN codes in response to a predetermined PN clock; an I channeldespreader for multiplying the digital converted I channel output fromthe analog-digital converter by the first and second PN codes and thenoutputting a band despreaded I channel signal; a Q channel despreaderfor multiplying the digital converted Q channel output from theanalog-digital converter by the first and second PN codes and thenoutputting a band despreaded Q channel signal; a PN code sync controllerfor Walsh- demodulating the band despreaded I channel and Q channelsignals in response to the first Walsh code, detecting the PN code syncstatus of the Walsh-demodulated I channel and Q channel signals and thenoutputting a PN clock corresponding to the PN code sync status; a Walshan orthogonal code generator for generating first and second Walsh codeshaving respective Walsh orthogonal code systems; a first Walshdemodulator for outputting first and second I channel signals which havebeen Walsh demodulated by the first and second Walsh codes; a secondWalsh orthogonal code systems; for outputting first and second Q channelsignals which have been Walsh- demodulated by the first and second Walshorthogonal codes; an accumulator and dump circuit for accumulating anddumping the Walsh- demodulated first and second I channel signals andfirst and second Q channel signals; a combiner for receiving the firstand second I channel signals and first and second Q channel signalsoutput from the accumulator and dump circuit, and multiplying the firstI channel signal by the second I channel signal to output a combined Ichannel signal and the first Q channel signal by the second Q channelsignal to output a combined Q channel signal; and a data decider forobtaining a difference value between the I channel signal and Q channelsignal output from the combiner and then deciding and outputting thedata corresponding to the phase of the difference value.

The present invention is more specifically described in the followingparagraphs by reference to the drawings attached only by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present invention, and many of theattendant advantages thereof, will become readily apparent as the samebecomes better understood by reference to the following detaileddescription when considered in conjunction with the accompanyingdrawings in which like reference symbols indicate the same or similarcomponents, wherein:

FIG. 1 is a block diagram showing construction of a transmitter for aspread spectrum communication system using a conventional DPSKmodulation method;

FIG. 2 is a block diagram showing construction a data transmitter of aspread spectrum communication system using a pilot channel according toa preferred embodiment of the present invention; and

FIG. 2A is a block schematic diagram illustrating the spreader stage ofthe communication system shown in FIG. 2; and

FIG. 3 is a block diagram showing construction of a data receiver of thespread spectrum communication system using the pilot channel accordingto the preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings and particularly to FIG. 1, whichillustrates a typical transmitter in a spread spectrum communicationsystem using a conventional differential phase-shift keying (DPSK)modulation technique. The transmitter includes a DPSK encoder 102 fordifferential-modulating input baseband data; a PN code generator 103 forgenerating a PN code sequence; a band spreader 104 for band spreadingthe differentially modulated data by multi-plying the differentiallymodulated data by the PN code sequence; a finite impulse response(hereinafter referred to as an “FIR”) filter 105 connected to the bandspreader 104, for filtering the band spreaded data; a D/A converter 106and a LPF 107 serially connected to the FIR filter 105, for convertingthe band spreaded data into an analog signal and low-pass filtering theanalog signal; and a mixer 109 for multiplying the output of the LPF 107by a carrier signal cosW_(c)t for propagation to free space through abandpass filter (hereinafter referred to as an “BPF”) 110, an amplifier111 and an antenna 112.

The advantage of employing a conventional DPSK modulation technique tomodulate the baseband data is that the spread spectrum communicationsystem is enabled to asynchronously detect the modulated datatransmitted from a transmitting side during the data demodulation at areceiving side. In this DPSK modulation spread spectrum communicationsystem, however, we have discovered that bit error tends to propagateduring the demodulation stage. For example, one bit error during thedemodulation stage may result in a two bit error. Consequently, thiserror propagation deteriorates the overall system performance. Moreover,we have observed that it is difficult to adjust the PN codesynchronization at a receiving side, as the modulated PN code and notpure PN code is transmitted at a transmitting side. Consequently, thetime required to establish initial synchronization has not effectivelyimproved.

As a result, the present invention envisions a spread spectrumcommunication system in which the PN code synchronization can beachieved with the pure PN code received at a receiving side in order tominimize the PN code acquisition time and the bit error rates. Thespread spectrum communication system according to the present inventioncontemplates upon a pilot channel in addition to a data channel, inwhich pure, unmodulated PN code can be transmitted therein foracquisition or tracking purposed at a receiving side. The signal to betransmitted in a spread spectrum communication system utilizing a pilotchannel according to the present invention may be largely divided into apilot signal and data. The data is an information signal, and the pilotsignal representing a binary bit of “1” is an additional informationsignal used for establishing initial PN code synchronization at areceiving side. According to the present invention, the pilot channeland the data channel are separated by a Walsh code sequence.

In the spread spectrum communication system utilizing the pilot channelaccording to the present invention, as the baseband data and the pilotsignal are simultaneously transmitted, the synchronous demodulation ofthe baseband data can be performed by the pilot signal. Moreover, as thepilot signal to be transmitted at a transmitting side is always “1”, theI channel and Q channel PN codes in a pilot channel are pure,unmodulated PN codes. Thus, the PN code synchronization can beestablished at a receiving side by the pure, unmodulated PN codes.

TurningTurn now to FIG. 2 which illustrates FIGS. 2 and 2A thatillustrate a data transmitter of the spread spectrum communicationsystem utilizing the pilot channel as constructed according to apreferred embodiment of the present invention.

As shown in FIG. 2FIGS. 2 and 2A, the data transmitter includes a firstpilot Walsh code generator 203 and a first traffic Walsh code generator206 for generating a first and a second Walsh codes, respectively usingWalsh functions represented by a set of orthogonal binary sequences thatcan be easily generated by means well known in the art. Therefore, aWalsh code is generally called an “orthogonal code”. A first multiplier202 modulates a pilot signal according to the first Walsh code generatedfrom the pilot Walsh code generator 203 in order to generate aWalsh-modulated pilot signal. A second multiplier 205 modulates basebanddata to be transmitted according to the second Walsh code generated fromthe traffic Walsh code generator 206 in order to generateWalsh-modulated data.

As in-phase (I) channel PN code generator 207 generates an I channel PNcode, and a quadrature-phase (Q) channel PN code generator 208 generatesa Q channel PN code. A third multiplier 209 multiplies theWalsh-modulated pilot signal according to the I channel PN code in orderto generate an I channel band spreaded spread pilot signal. A fourthmultiplier 210 multiplies the Walsh-modulated pilot signal according tothe Q channel PN code in order to generate a Q channel band spreadedspread pilot signal. A fifth multiplier 211 multiplies theWalsh-modulated data according to the I channel PN code in order togenerate I channel band spreaded spread data. A sixth multiplier 212multiplies the Q channel PN code by a predetermined value “−1” in orderto generate an inverted −Q channel PN code. A seventh multiplier 214multiplies the Walsh-modulated data according to the −O channel PN codein order to generate −Q channel band spreaded spread data.

A first FIR filter 215 finite impulse response filters the output of thethird multiplier 209. A second FIR filter 216 finite impulse responsefilters the output of the fourth multiplier 210. A third FIR filter 217finite impulse response filters the output of the seventh multiplier214. A fourth FIR filter 218 finite impulse response filters the outputof the fifth multiplier 211. The first, second, third, and fourth FIRfilters are used to reduce the peaks of the power spectrum density ofthe transmitted signal and to conceal the transmitted signal from thenoise in the communication channel.

A first added 219 combines the output signal of the first FIR filter 215with the output signal of the third FIR filter 217. A second adder 220combines the output signal of the second FIR filter 216 with the outputsignal of the fourth FIR filter 218. A first D/A converter 221 convertsthe output of the first added 219 into an analog signal. A second D/Aconverter 222 converts the output of the second adder 220 into an analogsignal.

First and second LPFs 223 and 224 respectively low-pass filter theoutputs of the first and second D/A converter 221 and 222. An eighthmultiplier 225 multiplies the output of the first LPF 223 for an Ichannel with an in-phase component cosW_(IF)t of anintermediate-frequency. A ninth multiplier 228 multiplies the output ofthe second LPF 224 for a Q channel with a quadrature-phase componentsinW_(IF)t of the intermediate frequency. A third adder 229 combines theoutput of the eighth multiplier 225 with the output of the ninthmultiplier 228. A tenth multiplier 230 multiplies the output of thethird adder 229 by a carrier signal cosW_(RF)t. A first BPF 232band-pass filters the output of the tenth multiplier 230. An amplifier233 amplifies the band-pass filtered signal in accordance with apredetermined amplification ratio in order to generate a spread spectrumsignal to be transmitted via an antenna 234.

As described above, the first input signal is multiplied by the firstspreading code signal to produce a first output signal, the first inputsignal is multiplied by an inverted code of the second spreading codesignal to produce a third output signal, the first input signal ismultiplied by the first spreading code signal to produce a fourth outputsignal, the first output signal is added to the third output signal, andthen the second output signal is added to the fourth output signal, sothat the above spreaded spectrum circuit of the communication systemcould effectively reduce a value of PAR that should be inevitably takeninto account upon design of a power amplifier.

The overall operation of this spread spectrum circuit will besubstantially similar to that of a spreading circuit in which a secondspreading code signal is directly multiplied by a second input signal totherefrom produce a third output signal and the third output signal issubtracted from the first input signal. The above spread spectrumcircuit is often referred to in the art as a “complex spreader”.

Further, the spread spectrum circuit preferably includes a constructionto receive a signal “−1” in the sixth multiplier 212 for inverting thesecond spreading code signal.

According to the spread spectrum circuit of the present invention, PARcan be effectively reduced as it allows a phase only of an input signalto be revolved to a phase of PN code, without making any changes to amagnitude of the input signal. Hence, it is appreciated that when PNcode is used for a signal spreading circuit as described above, a phaseof the PN code does not affect a magnitude of an input signal, therebykeeping the original magnitude of input signal as it was and decreasingPAR of the output signals.

FIG. 3 illustrates a data receiver of the spread spectrum communicationsystem utilizing the pilot channel as constructed according to thepreferred embodiment of the present invention.

As shown in FIG. 3, the data receiver includes a low noise amplifier(LNA) 302 serving as a high frequency amplifier for amplifying a spreadspectrum signal received from an antenna 301. A second BPF 303 band-passfilters the amplified spread spectrum signal. An eleventh multiplier 304multiplies the band-pass filtered signal with a carrier signalcosW_(RF)t in order to generate an intermediate frequency signal. Atwelfth multiplier 306 multiplies the output signal of the eleventhmultiplier 304 with an in-phase component cosW_(IF)t of the intermediatefrequency. A thirteenth multiplier 308 multiplies the output signal ofthe eleventh multiplier 304 with a quadrature-phase component sinW_(IF)tof the intermediate frequency.

Third and fourth LPFs 310 and 311 low-pass filter the output signals ofthe twelfth and thirteenth multipliers 306 and 308. First and second A/Dconverters 312 and 313 respectively convert the low-pass filteredsignals into digital signals. An I channel and Q channel PN codegenerator 314 generates I channel and Q channel PN codes in response toa predetermined PN clock.

A first despreader 315 in a form of a multiplier, multiplies the outputsignal of the first A/D converter 312 according to the I channel and Qchannel PN codes in order to generate a despreaded I channel signalI(t). A second despreader 316 in a form of a multiplier, multiplies theoutput signal of the second A/D converter 313 according to the I channeland Q channel PN codes in order to generate a despreaded Q channelsignal Q(t). A second pilot Walsh code generator 317 generates a firstWalsh code according to a first set of Walsh code functions. A secondtraffic Walsh code generator 318 generates a second Walsh code accordingto a second set of Walsh code functions. The first and second Walshcodes used in the receiver are identical to the Walsh codes used in thetransmitter as shown in FIG. 2.

A fourteenth multiplier 319 multiplies the despreaded I channel signalI(t) according to the first Walsh code in order to generate aWalsh-demodulated I channel signal I(t). A fifteenth multiplier 320multiplies the despreaded Q channel signal Q(t) according to the firstWalsh code in order to generate a Walsh-demodulated Q channel signalQ(t). An initial sync and sync detector 321 receives theWalsh-demodulated signals I(t) and Q(t) output from the fourteenth andfifteenth multipliers 319 and 320, detects the PN code synchronizationstate of the Walsh-demodulated signals I(t) and Q(t) in order togenerate a synchronization detection signal in correspondence with thePN code synchronization state.

A PN clock controller 322 outputs a clock control signal correspondingto the synchronization detection signal, A PN clock generator 323generates the PN clock for controlling the generation of the I channeland Q channel PN codes in response to the clock control signal. Asixteenth multiplier 24 multiplies the Q channel signal Q(t) output fromthe second despreaded 316 according to the first Walsh code. Aseventeenth multiplier 325 multiplies the I channel signal I(t) outputfrom the first despreader 315 according to the first Walsh code. Aneighteenth multiplier 326 multiplies the Q channel signal Q(t) outputfrom the second despreader 316 according to the second Walsh code. Anineteenth multiplier 327 multiplies the I channel signal I(t) outputfrom the first despreaded 315 according to the second Walsh code.

First, second, third, and fourth accumulator and dump circuits 328, 329,330, 331 respectively accumulate the output signals of the sixteenth,seventeenth, eighteenth, and nineteenth multipliers 324 and 327 for apredetermined symbol duration. A twentieth multiplier 332 multiplies theoutput signal of the second accumulator and dump circuit 329 with theoutput signal of the third accumulator and dump circuit 330. Atwenty-first multiplier 333 multiplies the output signal of the firstaccumulator and dump circuit 328 with the output signal of the fourthaccumulator and dump circuit 331. A subtracter 334 subtracts the outputsignal of the twenty-first multiplier 333 from the output signal of thetwentieth multiplier 332. A decider 335 detects the phase of data fromthe output signal of the subtracter 334 in order to generate demodulateddata.

The operation of the data transmitter and receiver of the spreadspectrum communication system utilizing the pilot channel according tothe preferred embodiment of the present invention will now be describedin detail with reference to FIGS. 2, 2A and 3.

In the spread spectrum communication system utilizing the pilot channelaccording to the present invention, the transmitted signal is comprisedof the pilot signal and baseband data as previously described. The pilotsignal component forms I channel signal component, and the traffic datacomponent forms Q channel signal component.

The pilot signal and the baseband data are respectively multiplied inaccordance with the outputs of the pilot and traffic Walsh codegenerators 203 and 206 at the first and second multipliers 202 and 205,respectively. Each output of the first and second multipliers 202 and205 is separated into the I and Q channels. That is, the output of thefirst multiplier 202 is multiplied according to the I channel PN codegenerated from the I channel PN code generator 207 at the thirdmultiplier 209, and according to the Q channel PN code generated fromthe Q channel PN code generator 208 at the fourth multiplier 210.Similarly, the output of the second multiplier 205 is multipliedaccording to the I channel PN code generated from the I channel PN codegenerator 207 at the fifth multiplier 211, according to the −Q channelPN code generated from the Q channel PN code generator 208 by way of thesixth multiplier 212 at the seventh multiplier 214.

The outputs of the third, fourth, seventh and fifth multipliers 209,210, 214 and 211 are respectively filtered through the first, second,third, and fourth FIR filters 215, 216, 217, 218. The first adder 219 asan I channel adder, combines the output signals of the first and thirdFIR filters 215 and 217 for an analog conversion by the first D/Aconverter 221. The second adder 220 as a Q channel adder, combined theoutput signals of the second and fourth FIR filters 216 and 218 for ananalog conversion by the second D/A converter 222.

The output of the first D/A converter 221 of an I channel component andthe output of the second D/A converter 222 of a Q channel component arethe signals in which the pilot and data signal components are combined,and are respectively passed through the first and second LPFs 223 and224. The output of the first LPF 223 is multiplied according to anin-phase component cosW_(IF)t of the intermediate frequency at theeighth multiplier 225, and the output of the second LPF 224 ismultiplied according to a quadrature-phase component sinW_(IF)t of theintermediate frequency at the ninth multiplier 228. The outputs of theeighth and ninth multipliers 225 and 228 are added at the third adder229, and the added signal is multiplied by the carrier signal cosW_(RF)tat the tenth multiplier 230, assuming that, for example, W_(c) is acarrier frequency, W_(c)=Wn_(IF)+W_(RF). The output of the tenthmultiplier 230 is passed through the first BPR 232, amplified at theamplifier 233, and then propagated to the free space through the antenna234.

At the receiver side, the spread spectrum signal received via theantenna 301 is passed to the eleventh multiplier 304 through an LNA 302and a second BPF 303. At the eleventh multiplier 304, the receivedspread spectrum signal is multiplied according to the carrier signalcosW_(RF)t, and converted into the intermediate-frequency signal. Theoutput of the eleventh multiplier 304 is multiplied according to anin-phase component cosW_(IF)t of the intermediate frequency at thetwelfth multiplier 306, and according a quadrature-phase componentsinW_(IF)t of the intermediate frequency at the thirteenth multiplier308, and converted into the I channel and Q channel spreaded signalsthrough the third and fourth LPFs 310 and 311. The outputs of the thirdand fourth LPFs 310 and 311 are converted into the digital signalsthrough the first and second A/D converters 312 and 313. The digitalsignals are respectively multiplied by the I channel and Q channel PNcodes, and despreaded at the first and second despreaders 315 and 316.The PN code component is removed from the despreaded signals by the Ichannel and Q channel PN codes. Thereafter, the fourteenth multiplier319 multiplies the despreaded output signal of the first despreader 315by the first Walsh code. The fifteenth multiplier 320 multiplies thedespreaded output signal of the second despreader 316 by the first Walshcode.

The outputs of the fourteenth and fifteenth multipliers 319 and 320 areapplied to the initial sync and sync detector 321 to establish the PNcode synchronization and synchronization detection operation. The outputof the initial sync and sync detector 321 is applied to the PN clockcontroller 322 for controlling the PN clock generator 323 to generatethe PN clock which controls the generation timing of the PN codes of theI channel and Q channel PN code generator 314.

If the PN code synchronization is established at the initialsynchronization and synchronization detector 321, the demodulation ofthe despreaded output signals of the first and second despreaders 315and 316 is performed to obtain demodulated data.

The output signal of the first despreader 315 is multiplied by the firstand second Walsh codes at the seventeenth and nineteenth multipliers 325and 327. The output signal of the second despreader 316 is multiplied bythe first and second Walsh codes at the sixteenth and eighteenthmultipliers 324 and 326.

Thus, the outputs of the sixteenth and seventeenth multipliers 324 and325 are pilot signal components and the outputs of the eighteenth andnineteenth multipliers 326 and 327 are data signal components. Theoutputs of the sixteenth, seventeenth, eighteenth, and nineteenthmultipliers 324 to 327 are respectively accumulated and dumped at thefirst, second, third, and fourth accumulator and dump circuits 328 to331. The outputs of the second and third accumulator and dump circuits329 and 330 are multiplied at the twentieth multiplier 332, and theoutputs of the first and fourth accumulator and dump circuits 328 and331 are multiplied at the twenty first multiplier 333.

The subtractor 334 subtracts the output of the twenty-first multiplier333 from the output of the twentieth multiplier 332 in order to generatea subtracted value. The decider 335 detects the data phase from thesubtracted value of the subtracter 334 in order to generate demodulateddata.

In short, as the spread spectrum communication system constructedaccording to the present invention seeks to transmit the pilot signalrepresenting a binary bit of “1” in a pilot channel in addition to theinformation signal so that the pilot signal can be used for PN codeacquisition at a receiving side. This is because the pilot signal to betransmitted is always “1”, and the PN codes at a transmitting side arenot modulated but remain pure and unmodulated for transmission throughthe pilot channel using the Walsh code.

As described above, the present invention is advantageous in that, asthe PN code synchronization is established using the pure PN codes, thecode acquisition can be easily improved with a lower bit error rate, andthe time required to establish initial synchronization can beeffectively enhanced. Moreover, another advantage of the presentinvention is that the pilot channel and the data channel are easilyseparated by the Walsh codes output from the Walsh code generators.

While there have been illustrated and described what are considered tobe preferred embodiments of the present invention, it will be understoodby those skilled in the art that various changes and modifications maybe made, and equivalents may be substituted for elements thereof withoutdeparting from the true scope of the present invention. In addition,many modifications may be made to adapt a particular situation to theteaching of the present invention without departing from the centralscope thereof. Therefore, it is intended that the present invention notbe limited to the particular embodiment disclosed as the best modecontemplated for carrying out the present invention, but that thepresent invention includes all embodiments falling within the scope ofthe appended claims.

What is claimed is:
 1. A spread spectrum communication system,comprising: a pilot channel signal generator for generating a pilotsignal exhibiting a predetermined binary value; a pseudo-random noisegenerator for generating first and second pseudo-random noise codes inresponse to a pseudo-random noise clock ; first Walshorthogonal codegenerator means for generating a first Walshorthogonal code according toa first set of Walshorthogonal code functions, and generating a secondWalshorthogonal code according to a second set of Walshorthogonal codefunctions; modulator means coupled to receive an input informationsignal and the pilot signal, for modulating the pilot signal accordingto the first Walsh orthogonal code and modulating the input informationsignal according to the second Walsh orthogonal code to generate amodulated pilot signal and a modulated information signal, respectively;and spreader means for band spreading the modulated pilot signal and themodulated information signal with each of the first and secondpseudo-random noise codes to generate a spread spectrum signal to betransmitted via a communication channel.
 2. The spread spectrumcommunication system of claim 1, wherein said spreader means comprises:a first multiplier for multiplying the modulated pilot signal with thefirst pseudo-random noise code for an in-phase channel to produce anin-phase band spreaded spread pilot signal; a second multiplier formultiplying the modulated pilot signal with the second pseudo-randomnoise code for a quadrature-phase channel to produce a quadrature-phaseband spreaded spread pilot signal; a third multiplier for multiplyingthe second pseudo-random noise code with a predetermined value toproduce an inverted pseudo-random noise code; a fourth multiplier formultiplying the modulated information signal with the firstpseudo-random noise code for an in-phase channel to produce an in-phaseband spreaded spread information signal; a fifth multiplier formultiplying the modulated information signal with the invertedpseudo-random noise code for a quadrature-phase channel to produce aquadrature-phase band spreaded spread information signal; and a firstset of finite impulse response filters connected to the first, second,fourth, and fifth multipliers, for reducing the peaks of the powerspectrum density of the in-phase band spreaded pilot and informationsignals and the quadrature-phase band spreaded pilot and informationsignals; adder means for combining the in-phase band spreaded spreadpilot and signal with the quadrature-phase band spread informationsignals signal and the quadrature-phase band spreaded spread pilot andsignal with the in-phase information signals signal to produce anin-phase signal and a quadrature-phase signal, respectively, forproducing said spread spectrum signal to be transmitted via thecommunication channel; and upconverter means for upconverting thein-phase signal and the quadrature-phase signal and producing saidspread spectrum signal to be transmitted via the communication channel .3. The spread spectrum communication system of claim 2, wherein saidupconverter means comprises: converter means for generating an in-phaseanalog signal and a quadrature-phase analog signal by converting thein-phase signal and the quadrature-phase signal into an analog format;filter means for generating an in-phase filtered signal and aquadrature-phase filtered signal by low-pass filtering the in-phaseanalog signal and the quadrature-phase analog signal; first mixer meansfor multiplying the in-phase filtered signal with an in-phase componentof an intermediate frequency signal and the quadrature-phase filteredsignal with a quadrature-phase component of the intermediate frequencysignal, respectively, and for generating a combined signal based uponthe combination of the multiplied results; second mixer means forgenerating said spread spectrum signal by multiplying the combinedsignal with a carrier frequency; and amplifier means for amplifying saidspread spectrum signal prior to transmission via said communicationchannel.
 4. The spread spectrum communication system of claim 1, furthercomprising: means for receiving said spread spectrum signal from saidcommunication channel having a received pseudo-random noise code and areceived pilot signal modulated therein, and separating an in-phasesignal and an quadrature-phase signal therefrom; a second pseudo-randomnoise generator for generating the first and second pseudo-noise codes,respectively, in response to the pseudo-random noise clock; despreadermeans for band despreading the in-phase signal and the quadrature-phasesignal with each of the first and second pseudo-random noise codes togenerate a despreaded in-phase signal and a despreaded quadrature-phasesignal; second Walsh code generator means for generating the first Walshcode according to a first set of Walsh functions, and generating thesecond Walsh code signal according to a second set of Walsh functions;first demodulator means for demodulating the despreaded in-phase signaland the despreaded quadrature-phase signal according to the first Walshcode into a demodulated in-phase signal and a demodulatedquadrature-phase signal; pesudo-random noise code control means forreceiving the demodulated in-phase signal and the demodulatedquadrature-phase signal, and establishing initial synchronizationbetween the received pseudo-random noise code modulated in the receivedspread spectrum signal and the first and second pseudo-random noisecodes by generating the pseudo-random noise clock to control generationof the first and second pseudo-random noise codes; and seconddemodulator means for demodulating the despreaded in-phase signal andthe despreaded quadrature-phase signal according to the first and secondWalsh codes to produce a demodulated baseband signal.
 5. The spreadspectrum communication system of claim 4, wherein said receiving meanscomprises: bandpass filter means for generating a bandpass filteredsignal by bandpass filtering the received spread spectrum signal fromsaid communication channel; first mixer means for generating anintermediate frequency signal by multiplying the bandpass filteredsignal with a carrier frequency; second mixer means for generating thein-phase signal and the quadrature-phase signal by multiplying theintermediate frequency signal with an in-phase channel component and aquadrature-phase channel component; low-pass filter means for low-passfiltering the in-phase signal and the quadrature-phase signal; and thequadrature-phase in a digital format.
 6. The spread spectrumcommunication system of claim 5, wherein said pseudo-random noise codecontrol means comprises: pseudo-random code acquisition means forestablishing initial synchronization between the received pseudo-randomnoise code modulated in the received spread spectrum signal and thefirst and second pseudo-random noise codes; pseudo-random code detectormeans for detecting the pseudo-random noise codes of the demodulatedin-phase and quadrature-phase signals and generating a sync detectionsignal; pseudo-random noise clock control means for generating a clockcontrol signal corresponding to the sync detection signal; andpseudo-random noise clock generator means for generating thepseudo-random noise clock for controlling generation of the first andsecond pseudo-random noise codes.
 7. The spread spectrum communicationsystem of claim 6 wherein said second demodulator means comprises: afirst multiplier for generating a first multiplied signal by multiplyingthe despreaded quadrature-phase signal with the first Walsh code; asecond multiplier for generating a second multiplied signal bymultiplying the despreaded in-phase signal with the first Walsh code; athird multiplier for generating a third multiplied signal by multiplyingthe despreaded quadrature-phase signal with the second Walsh code; afourth multiplier for generating a fourth multiplied signal bymultiplying the despreaded in-phase signal with the second Walsh code;accumulator and dump means connected to the first, second, third, andfourth multipliers, for accumulating the first, second, third, andfourth multiplied signals for a predetermined symbol duration; fifthmultiplier for generating a combined in-phase signal by multiplying thefirst multiplied signal accumulated for said predetermined symbolduration with the fourth multiplied signal accumulated for saidpredetermined symbol duration; a sixth multiplier for generating acombined quadrature-phase signal by multiplying the second multipliedsignal accumulated for said predetermined symbol duration with the thirdmultiplied signal accumulated for said predetermined symbol duration;and means for obtaining a difference value between the combined in-phasesignal and the combined quadrature-phase signal and generating saiddemodulated baseband signal corresponding to the phase of the differencevalue.
 8. The spread spectrum communication system of claim 4, whereinsaid pseudo-random noise code control means comprises: pseudo-randomcode acquisition means for establishing initial synchronization betweenthe received pseudo-random noise code modulated in the received spreadspectrum signal and the first and second pseudo-random noise codes;pseudo-random code detector means for detecting the pseudo-random noisecodes of the demodulated in-phase and quadrature-phase signals andgenerating a sync detection signal; pseudo-random noise clock controlmeans for generating a clock control signal corresponding to the syncdetection signal; and pseudo-random noise clock generator means forgenerating the pseudo-random noise clock for controlling generation ofthe first and second pseudo-random noise codes.
 9. The spread spectrumcommunication system of claim 4, wherein said second demodulator meanscomprises: a first multiplier for generating a first multiplied signalby multiplying the despreaded quadrature-phase signal with the firstWalsh code; a second multiplier for generating a second multipliedsignal by multiplying the despreaded in-phase signal with the firstWalsh code; a third multiplier for generating a third multiplied signalby multiplying the despreaded quadrature-phase signal with the secondWalsh code; a fourth multiplier for generating a fourth multipliedsignal by multiplying the despreaded in-phase signal with the secondWalsh code; accumulator and dump means connected to the first, second,third, and fourth multipliers, for accumulating the first, second,third, and fourth multiplied signals for a predetermined symbolduration; a fifth multiplier for generating a combined in-phase signalby multiplying the first multiplied signal accumulated for saidpredetermined symbol duration with the fourth multiplied signalaccumulated for said predetermined symbol duration; a sixth multiplierfor generating a combined quadrature-phase signal by multiplying thesecond multiplied signal accumulated for said predetermined symbolduration with the third multiplied signal accumulated for saidpredetermined symbol duration; and means for obtaining a differencevalue between the combined in-phase signal and the combinedquadrature-phase signal and generating said demodulated baseband signalcorresponding to the phase of the difference value.
 10. A spreadspectrum receiver, comprising: means for receiving a spread spectrumsignal via an antenna having a pilot signal and an information signalspread by in-phase and quadrature-phase pseudo-random noise codes,respectively, a received pseudo-random noise code and a received pilotsignal modulated therein, and separating an in-phase signal and anquadrature-phase signal therefrom; pseudo-random noise generator meansfor generating first and second pseudo-random noise codes, respectively,in response to a pseudo-random noise clock; despreader means for banddespreading the in-phase signal and the quadrature-phase signal witheach of the first and second pseudo-random noise codes to generate adespreaded in-phase signal and a despreaded quadrature-phase signal;Walsh code generator means for generating a first Walsh orthogonal codeaccording to a first set of Walsh orthogonal code functions, andgenerating a second Walsh orthogonal code signal according to a secondset of Walsh orthogonal code functions; first demodulator means fordemodulating the despreaded in-phase signal and the despreadedquadrature-phase signal according to the first Walsh orthogonal codeinto a demodulated in-phase signal and a demodulated quadrature-phasesignal; pseudo-random noise code control means for receiving thedemodulated in-phase and quadrature-phase signals, and establishinginitial synchronization between the received pseudo-random noise codemodulated in the received spread spectrum signal in-phase andquadrature-phase pseudo-random noise codes and the first and secondpseudo-random noise codes by generating the pseudo-random noise clock tocontrol generation of the first and second pseudo-random noise codes;and second demodulator means for demodulating the despreaded in-phaseand quadrature-phase signals according to the first and second Walshorthogonal codes to produce a demodulated baseband signal.
 11. Thespread receiver of claim 10, wherein said receiving means comprises:bandpass filter means for generating a bandpass filtered signal bybandpass filtering the received spread spectrum signal via said antenna;first mixer means for generating an intermediate frequency signal bymultiplying the bandpass fibered filtered signal with a carrierfrequency; second mixer means for generating the in-phase signal and thequadrature-phase signal by multiplying the intermediate frequency signalwith an in-phase channel component and a quadrature-phase channelcomponent; low-pass filter means for low-pass filtering the in-phasesignal and the quadrature-phase signal; and converter means forconverting the in-phase signal and the quadrature-phase signal in adigital format.
 12. The spread spectrum receiver of claim 10, whereinsaid pseudo-random noise code control means comprises: pseudo-randomnoise code acquisition means for establishing initial synchronizationbetween the received pseudo-random noise code modulated in the receivedspread spectrum signal in-phase and quadrature-phase pseudo-random noisecodes and the first and second pseudo-random noise codes; pseudo-randomnoise code detector means for detecting the in-phase andquadrature-phase pseudo-random noise codes of the demodulated in-phaseand quadrature-phase signals and generating a sync detection signal;pseudo-random noise clock control means for generating a clock controlsignal corresponding to the sync detection signal; and pseudo-randomnoise clock generator means for generating the pseudo-random noise clockfor controlling generation of the first and second pseudo-random noisecodes.
 13. The spread spectrum receiver of claim 10, wherein said seconddemodulator means comprises: a first multiplier for generating a firstmultiplied signal by multiplying the despreaded quadrature-phase signalwith the first Walsh orthogonal code; a second multiplier for generatinga second multiplied signal by multiplying the despreaded in-phase signalwith the first Walsh orthogonal code; a third multiplier for generatinga third multiplied signal by multiplying the despreaded quadrature-phasesignal with the second Walsh orthogonal code; a fourth multiplier forgenerating a fourth multiplied signal by multiplying the despreadedin-phase signal with the second Walsh orthogonal code; accumulator anddump means connected to the first, second, third, and fourthmultipliers, for accumulating the first, second, third, and fourthmultiplied signals for a predetermined symbol duration; a fifthmultiplier for generating a combined in-phase signal by multiplying thefirst multiplied signal accumulated for said predetermined symbolduration with the fourth multiplied signal accumulated for saidpredetermined symbol duration; a sixth multiplier for generating acombined quadrature-phase signal by multiplying the second multipliedsignal accumulated for said predetermined symbol duration with the thirdmultiplied signal accumulated for said predetermined symbol duration;and means for obtaining a difference value between the combined in-phasesignal and the combined quadrature-phase signal and generating saiddemodulated baseband signal corresponding to the phase of the differencevalue.
 14. The spread spectrum receiver of claim 11, wherein saidpseudo-random noise code control means comprises: pseudo-random noisecode acquisition means for establishing initial synchronization betweenthe received pseudo-random noise code modulated in the received spreadspectrum signal in-phase and quadrature-phase pseudo-random noise codesand the first and second pseudo-random noise codes; pseudo-random noisecode detector means for detecting the in-phase and quadrature-phasepseudo-random noise codes of the demodulated in-phase andquadrature-phase signals and generating a sync detection signal;pseudo-random noise clock control means for generating a clock controlsignal corresponding to the snyc detection signal; and pseudo-randomnoise clock generator means for generating the pseudo-random noise clockfor controlling generation of the first and second pseudo-random noisecodes.
 15. A transmitter of a spread spectrum communication system usinga pilot channel, comprising: Walshorthogonal code generating means forgenerating first and second Walshorthogonal codes having respective codesystems; Walsh modulating means for multiplying a predetermined pilotsignal and information signal to be transmitted respectively by saidfirst and second Walsh orthogonal codes and then generating Walsh-modulated pilot and information signals; PN code generating means forgenerating predetermined first and second pseudo-random noise (PN)codes; first band spread means for multiplying said Walsh- modulatedpilot signal by said first and second PN codes to produce band spreadedspread I channel and Q channel pilot signals; second band spread meansfor multiplying said Walsh- modulated information signals signal by aninverted second PN code and said first PN code to produce band spreadedspread I channel and Q channel information signals; finite impulseresponse filtering means for finite impulse response filtering and bandspreaded spread I channel and Q channel pilot signals and said band Ichannel and Q channel information signals; first converting means forcombining the filtered band spreaded spread I channel pilot signal andthe filtered band spreaded I spread Q channel information signal andthen converting into an I channel analog signal; second converting meansfor combining the filtered band spreaded spread Q channel pilot signaland the filtered band spreaded Q spread I channel information signal andthen converting into a Q channel analog signal; a low-pass filter forlow-pass filtering said I channel and Q channel analog signals toproduce I channel and Q channel low-pass filtered signals; a first mixerfor multiplying said I channel low-pass filtered signal by an in-phasecomponent of an intermediate frequency signal and multiplying said Qchannel low-pass filtered signal by an a quadrature-phase component ofsaid intermediate frequency signal, and then combining the I channel andQ channel multiplied signals which have been mixed with saidintermediate frequency signal; a second mixer for multiplying an outputsignal of said first mixer by a radio frequency signal; a band-passfilter for band-pass filtering an output signal of said second mixer;and an amplifier for amplifying an output signal of said band-passfilter in accordance with a predetermined amplification ratio to producea baseband signal.
 16. The transmitter of claim 15, wherein said secondband spread means comprises: a first multiplier for multiplying saidsecond PN code by “−1” to produce said inverted second PN code; a secondmultiplier for multiplying said Walsh- modulated information signal byaid inverted second PN code to produce the band spreaded spread Qchannel information signal; and a third multiplier for multiplying saidWalsh- modulated information signal by said first PN code to produce theband spreaded spread I channel information signal.
 17. A receiver of aspread spectrum communication system using a pilot channel, comprising:means for receiving a spread spectrum signal from an antenna; a firstfilter for generting a band-pass filtered signal by band-pass filteringthe received spread spectrum signal; a first mixer for multiplying theband-pass filtered signal by a radio-frequency signal and thenconverting into an intermediate-frequency signal; a second mixer formultiplying the intermediate-frequency signal by an in-phase componentand a quadrature-phase component of an intermediate frequency, andgenerating I channel and Q channel signals in which a carrier frequencyhas been removed; a second filter for generating low-pass filtered Ichannel and Q channel signals by low-pass filtering said I channel and Qchannel signals; converting means for converting the low-pass filtered Ichannel and Q channel signals into digital-converted I channel and Qchannel signals; PN code generating means for generating first andsecond PN codes having respective PN code systems in response to a PNclock; I channel despreader means for multiplying the digital-convertedI channel signal by said first and second PN codes, and generating adespreaded I channel signal; Q channel despreader means for multiplyingthe digital-converted Q channel signal by said first and second PNcodes, and generating a despreaded Q channel signal; Walshorthogonalcode generating means for generating first and second Walshorthogonalcodes having respective Walsh code systems; # PN code sync control meansfor Walsh- demodulating said despreaded I channel and Q channel signalswith said first Walsh orthogonal code, establishing sychronization ofthe Walsh demodulated I channel and Q channel signals, and generatingthe PN clock corresponding to said synchronization; first Walshdemodulating means for receiving and demodulating said despreaded Ichannel signal in accordance with said first and second Walsh orthogonalcodes to produce Walsh- demodulated first and second I channel signalsrespectively; second Walsh demodulating means for receiving anddemodulating said despreaded Q channel signal in accordance with saidfirst and second Walsh orthogonal codes to produce Walsh- demodulatedfirst and second Q channel signals respectively; combining means formultiplying the Walsh- demodulated first and second I channel signalsand multiplying the Walsh- demodulated first and second Q channelsignals to produce a combined I channel signal and a combined Q channelsignal; and data deciding means for obtaining a difference value betweensaid combined I channel and Q channel signals to produce a basebandsignal corresponding to the phase of said difference value.
 18. Thereceiver of claim 17, wherein said PN code sync control means comprises:third Walsh demodulating means for Walsh-demodulating said despreaded Ichannel and Q channel signals in accordance with said first Walshorthogonal code; initial sync and sync detection means for establishingsynchronization of the Walsh- demodulated first and second I channel andQ channel signals and generating a synchronization detection signalcorresponding to said synchronization; PN clock control means foroutputting a clock control signal corresponding to said synchronizationdetection signal; and PN clock generating means for generating the PNclock to control generation of said first and second PN codes under thecontrol of said clock control signal.
 19. A spreading circuit,comprising: a first spreader having a first input port, a second inputport, and an output port exhibiting a first output signal correspondingto a product of a first input signal and a first spreading code signalapplied to said first input port and said second input port,respectively, a second spreader having a third input port coupled tosaid first input port, a fourth input port, and an output portexhibiting a second output signal corresponding to a product of saidfirst input signal and a second spreading code signal applied to saidthird input port and said fourth input port, respectively; an inverterhaving a fifth input port coupled to said fourth input port, and anoutput port exhibiting a third output signal corresponding to aninversion of said second spreading code signal applied to said fifthinput port; a third spreader having a sixth input port coupled toreceive said third output signal, a seventh input port, and an outputport exhibiting a fourth output signal corresponding to a product of asecond input signal and said third output signal applied to said seventhinput port and said sixth input port, respectively; a fourth spreaderhaving an eighth input port coupled to said second input port, a ninthinput port coupled to said seventh input port, and an output portexhibiting a fifth output signal corresponding to a product of saidsecond input signal and said first spreading code signal applied to saidninth input port and said eighth input port, respectively; a first adderproviding a sixth output signal by combining said first output signaland said fourth output signal; and a second adder providing a seventhoutput signal by combining said second output signal and said fifthoutput signal.
 20. The spreading circuit of claim 19, wherein each ofsaid first, second, third and fourth spreader is a multiplier.
 21. Thespreading circuit of claim 19, further comprised of: a first multiplierdisposed to generate an eighth output signal by multiplying said sixthoutput signal by an in-phase component of an intermediate signal; asecond multiplier disposed to generate a ninth output signal bymultiplying said seventh output signal by a quadrature phase componentof said intermediate signal; and a third adder combining said eighthoutput signal and said ninth output signal.
 22. The spreading circuit ofclaim 19, further comprised of: a first multiplier disposed to generatean eighth output signal by multiplying said sixth output signal by anin-phase component of an intermediate signal; a second multiplierdisposed to generate a ninth output signal by multiplying said seventhoutput signal by a quadrature phase component of said intermediatesignal; a third adder generating a tenth output signal by combining saideighth output signal and said ninth output signal; and a thirdmultiplier disposed to multiply said tenth output signal by a carriersignal.
 23. The spreading circuit of claim 19, further comprised of: afirst generator providing said first spreading code signal, coupled tosaid second input port; and a second generator providing said secondspreading code signal, coupled to said fourth input port.
 24. Thespreading circuit of claim 19, further comprised of: a first generatorproviding said first spreading code signal, coupled to said second inputport; a second generator providing said second spreading code signal,coupled to said fourth input port; a third generator providing a firstorthogonal code; a fourth generator providing a second orthogonal code;a first multiplier disposed to apply said first input signal to saidfirst input port by multiplying said first orthogonal code by a firstapplied signal; and a second multiplier disposed to apply said secondinput signal to said seventh input port by multiplying said secondorthogonal code by a second applied signal.
 25. The spreading circuit ofclaim 21, further comprised of: a first generator providing said firstspreading code signal, coupled to said second input port; a secondgenerator providing said second spreading code signal, coupled to saidfourth input port; a third generator providing a first orthogonal code;a fourth generator providing a second orthogonal code; a thirdmultiplier disposed to apply said first input signal to said first inputport by multiplying said first orthogonal code by a second appliedsignal; and a fourth multiplier disposed to apply said second inputsignal to said seventh input port by multiplying said second orthogonalcode by a first applied signal.
 26. A complex spreading circuit,comprising: a first stage disposed to separately spread a first inputsignal by an in-phase pseudo-random noise code and a quadrature-phasepseudo-random noise code to provide respectively a first output signalcorresponding to a product of said first input signal and said in-phasepseudo-random noise code, and a second output signal corresponding to aproduct of said first input signal and said quadrature-phasepseudo-random noise code; a second stage disposed to separately spread asecond input signal by an inversion of said quadrature-phasepseudo-random noise code and by said in-phase pseudo-random noise code,to provide respectively a third output signal corresponding to a productof said second input signal and said inversion of said quadrature-phasepseudo-random noise code, and a fourth output signal corresponding to aproduct of said second input signal and said in-phase pseudo-randomnoise code; and a third stage providing a fifth output signal bycombining said first output signal with said third output signal, andproviding a sixth output signal by combining said second output signalwith said fourth output signal.
 27. The complex spreading circuit ofclaim 26, further comprised of a multiplier having a first input portcoupled to receive said quadrature-phase pseudo-random noise code and anoutput port exhibiting said inversion of said quadrature-phasepseudo-random noise code.
 28. The complex spreading circuit of claim 26,further comprised of: a first multiplier disposed to generate a seventhoutput signal by multiplying said fifth output signal by an in-phasecomponent of an intermediate signal; a second multiplier disposed togenerate an eighth output signal by multiplying said sixth output signalby a quadrature phase component of said intermediate signal; and anadder combining said seventh output signal and said eighth outputsignal.
 29. The complex spreading circuit of claim 26, further comprisedof: a first multiplier disposed to generate a seventh output signal bymultiplying said fifth output signal by an in-phase component of anintermediate signal; a second multiplier disposed to generate an eighthoutput signal by multiplying said sixth output signal by a quadraturephase component of said intermediate signal; an adder combining saidseventh output signal and said eighth output signal; and a thirdmultiplier disposed to multiply an output signal of said adder by acarrier signal.
 30. The complex spreading circuit of claim 26, furthercomprised of: a first generator providing a first orthogonal code; asecond generator providing a second orthogonal code; a first multiplierdisposed to generate said first input signal by modulating a firstreceived signal with said first orthogonal code; and a second multiplierdisposed to generate said second input signal by modulating a secondreceived signal with said second orthogonal code.
 31. The complexspreading circuit of claim 30, further comprised of: a third multiplierdisposed to generate a seventh output signal by multiplying said fifthoutput signal by an in-phase component of an intermediate signal; afourth multiplier disposed to generate an eighth output signal bymultiplying said sixth output signal by a quadrature phase component ofsaid intermediate signal; an adder combining said seventh output signaland said eighth output signal; and a fifth multiplier disposed tomultiply an output signal of said adder by a carrier signal.
 32. Amethod of spreading first and second input signals with first and secondspreading code signals in a transmitter of a spread spectrumcommunication system, comprising: spreading said first signal with saidfirst and second spreading code signals to produce first and secondspread signals, respectively; spreading said second signal with saidfirst and second spreading code signals to produce a third spread signaland an inversion of a fourth spread signal, respectively; producing afirst output spread signal by combining said inversion of said fourthspread signal and said first spread signal; and producing a secondoutput spread signal by combining said second spread signal and saidthird spread signal.
 33. A method of spreading first and second inputsignals in a transmitter of a spread spectrum communication system,comprising: spreading said first input signal with in-phase andquadrature-phase spreading code signals to produce first and secondspread signals, respectively; spreading said second input signal withsaid in-phase and quadrature-phase spreading code signals to produce athird spread signal and an inverted fourth spread signal, respectively;producing a first output spread signal by adding said inverted fourthspread signal and said first spread signal; and producing a secondoutput spread signal by adding said second spread signal and said thirdspread signal.
 34. A spread spectrum signal, comprising: a first signalin-phase spread produced by multiplying said first signal with anin-phase pseudo-random noise code, combined with a second signalquadrature-phase spread produced by multiplying said second signal withan inversion of a quadrature-phase pseudo-random noise code; and a firstsignal quadrature-phase spread produced by multiplying said first signalwith said quadrature-phase pseudo-random noise code, combined with saidsecond signal in-phase spread produced by multiplying said second signalwith said in-phase pseudo-random noise code.
 35. A method of spreadingfirst and second input signals with first and second spreading codesignals in a transmitter of a spread spectrum communication system,comprising: spreading said first signal with said first and secondspreading code signals to produce first and second spread signals,respectively; spreading said second signal with said first and secondspreading code signals to produce third and fourth spread signals,respectively; producing a first output spread signal by subtracting saidfourth spread signal from said first spread signal; and producing asecond output spread signal by adding said second spread signal and saidthird spread signal.
 36. A circuit for spreading first and second inputsignals with first and second spreading code signals in a tranmitter ofa spread spectrum communication system comprising: a first stagedisposed to spread said first input signal with said first and secondspreading code signals to produce first and second spread signals,respectively; a second stage disposed to spread said second input signalwith said first and second spreading code signals to produce a thirdspread signal and an inversion of a fourth spread signal, respectively;a third stage producing a first output spread signal by combining saidinversion of said fourth spread signal and said first spread signal; anda fourth stage producing a second output spread signal by combining saidsecond spread said and said third spread signal.
 37. A circuit forspreading first and second input signals in a transmitter of a spreadspectrum communication system, comprising: a first stage disposed tospread said first input signal with in-phase and quadrature-phasespreading code signals to produce first and second spread signals,respectively; a second stage disposed to spread said second input signalwith said in-phase and quadrature-phase spreading code signals toproduce a third spread signal and an inverted fourth spread signal,respectively; a third stage producing a first output spread signal byadding said inverted said fourth spread signal and said first spreadsignal; and a fourth stage producing a second output spread signal byadding said second spread signal and said third spread signal.
 38. Themethod of claim 32, further comprised of generating said inversion ofsaid fourth spread signal by inverting said second spreading codesignals prior to said spreading of said second signal with said secondspreading code signals.
 39. The method of claim 33, further comprised ofgenerating said inverted fourth spread signal by inverting saidquadrature-phase spreading code signals prior to said spreading of saidsecond input signal with said quadrature-phase spreading code signals.40. The circuit of claim 36, wherein said second stage further comprisesan inverter coupled to apply an inversion of said second spreading codesignals to produce said inversion of said fourth spread signal.
 41. Thecircuit of claim 37, wherein said second stage further comprises aninverter coupled to apply an inversion of said quadrature-phasespreading code signals to produce said inverted fourth spread signals.